Method of and apparatus for grinding moist material



Dec. 6, 1966 B. HELMING ET AL 3,289,950

METHOD OF AND APPARATUS FOR GRINDING MOIST MATERIAL Filed 0G11. 28, 1965 4 Sheets-Sheet l wasie gas A Q /7 r f/ moist charge l Laarse particles 1 Ol yV Il fine grinding f' drying /Q chamber fresh air aus r or .f g 5l @lV/1o g drying I warm gas chamber o o OO O Iaw 2C? ffqo @bfogoos 4 l loqngoucoog ocQygggoooOgjgOooo Q pgoooooo ooooovofbooo 0000 oOOD Q: 008Go particles I fine pa S Dec. 6, 1966 B. HELMING ET Al. 3,289,950

METHOD 0F AND APPARATUS FOR GRINDING MOIST MATERIAL Filed 001.. 28, 1963 4 Sheets-Sheet f?,

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/ drying ggg/:ggg- I I coarse material finish ground INVENTORS Dec. 6, 1966 B. HELMING ETAL 3,289,950

METHOD OF AND APPARATUS FOR GRINDING MOIST MATERIAL Filed OCT'. 28, 1963 4 ShGQS-Sheet, 3

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24 to afmophere Q l pre dried l material ,L/

sfter moist charge 27 cyclon de-duser ,l f g $`\26 30 Niue gas (drying gas) INVENTORS ernol /e/m in; Afef/,rfc /y/enfv e,

Dec. 6, 1966 B HELMING ET A1. 3,289,950

METHOD OF AND APPARATUS FOR GRINDING MOIST MATERIAL Filed Oct. 28, 1965 4 Sheets-Sheet 4 to al'mophere Fig. 5

de-dusfe-l cycion gr/fs arresier finish ground d 'm a 9 rylng A 905 2 i grinding A fresala M I chamber wurm gas drying chambe z ooo ooo bucket conveyer INVENTORS Bern a( e/v/y @MQW United States Patent O 3,289,950 METHOD F AND APPARATUS FOR GRINDING MOIST MATERIAL Bernd Helming, Neubeckum, Westphalia, and Heinrich Henne, Ennigerloh, Westphalia, Germany, assignors to Polysius G.m.b.H., Westphalia, Germany Filed Oct. 28, 1963, Ser. No. 319,934 Claims priority, application Germany, Dec. l2, 1962, P 30,758 12 Claims. (Cl. 241-18) The present invention relates to a method of and apparatus for grindingdrying moist material while employing a tube mill operating in a closed circuit with a sitter or separator, which tube mill has associated therewith a built-in drying chamber.

According to la heretofore known grinding-drying system comprising a combination of ball mill and hammer mill or impact mill and operating in Ia closed circuit, the moist material to be ground is first charged into a heated or non-heated hammer mill, impact mill or the like, `and then passed to a sifter or separator which may likewise be heated. The grits separated by the sifter then are passed to a ball mill the ground product of which is conveyed to the sitter in which, thus, the material from the hammer mill :and the material from the ball mill are sifted together, With combination arrangements of the above type, in some instances also the ball mill is heated for purposes of drying the material.

Grinding-drying installations combined of hammer or impact mills with a ball mill have caused considerable difficulties in practice due to the fact that when the material to be ground is rather moist and sticky, clogging and sticking of the material is encountered in the hammer mill or other mills operating by blow or impact, or such clogging and sticking occurs in the inlet and discharge lines of such mills. This clogging and sticking may interfere with the operation of the installation and even cause work stoppage. Efforts have, therefore been made to counteract these occurrences by heating the impact surface or by providing movable impact surfaces, but these efforts have either proved unsatisfactory in practice or they have yrequired rather expensive and complicated systems.

The additional drying in a heated sifter, which is carried out subsequently to the treatment of the material in the hammer mill, likewise results in considerable disadvantages. More specifically, the material pre-crushed by the hammer mill is still relatively coarse because it has not yet passed through the ball mill and consequently, it exerts a considerable wearing effect upon the sensitive inner structural members of the sifter, so that said structural members have to be exchanged relatively frequently. Furthermore, due to the influence of the hot drying gases, the sifter frequently suf-fers damages caused `by over-heating and warping inherent thereto.

It is also known, for purposes of g-rinding-drying, to employ an Iair flow tube mill in which the material to be ground is dried by conveying drying gases into the milling chamber, whereupon the material is conveyed in an air flow to a sifter. In view of the high flow resistance, the air flow tube mill consumes considerable energy. It is for this reason that it has been replaced by a grinddrying system according to which the circulation of the material is effected no longer in a gas or air flow but by mechanical means as, for instance, a bucket conveyor. Such an arrangement will, due to the considerably better degree of efficiency of the mechanical conveyance of the material, bring about a considerable reduction in the energy consumption of the grinding installation.

In an effort to dry the material to be ground as far as possible, prior to the material entering the grinding chamber proper, so that the material can be ground better,

ICC

it has been suggested to separate the drying and grinding in the tube mill from each other by inserting therebetween a dryirig chamber. However, it is a well-known fact that a certain speed of the ydrying gas or the air of the temperature of the atmosphere for discharging the grinding heat must not be exceeded since otherwise, the grinding operation will be interfered with. lThe material to be ground will, when the air or gas speed is too high, be discharged to an undesired extent in the air or gas flow. As a result thereof, in addition to the unfavorable influence upon the grinding operation, unnecessarily high energy is wasted for the passage of the gas.

On the other hand, for drying in the drying chamber which is built into tube mills of the above-mentioned type, there exists an optimum speed of the drying gas which, While being ideal for the drying will, when the material is rather moist, far exceeds the speed which is ideal for the grinding operation. Thus, if, in conformity with the heretofore employed practice, the drying gases are passed through the drying chamber, and subsequently through the grinding chamber, even though the drying heat has already been consumed, -it is unavoidable that unfavorable conditions are created either for the drying chamber or for the grinding chamber, or for both the drying and grinding chambers. Complete exploitation of the capacity of the drying chamber requires a high drying Volume and thus, high gas velocity. In the successively arranged grinding chamber, however, whose cross` section is reduced by approximately 50% by the charge, a considerably higher gas velocity will be created, to the detriment of the grinding operation, and a considerably higher energy consumption will result.

The above-mentioned drawback of the method makes itself, nowadays, particularly felt in View of the fact that there exists the tendency, in grinding-drying installations, to employ low temperature waste gases of rotary kilns and the Waste gases of coolers, for drying purposes. However, the lower the drying temperature, the greater the gas volume will be which 4is required in order to obtain the same drying output. The grinding output thus becomes more and more dependent on the drying output.

It is, therefore, an object of the present invention to provide a method of and device for drying-grinding moist material, which will overcome the above-mentioned drawback.

It is another object of this invention to provide a method and apparatus as set forth above, which will greatly increase the economy of the drying and grinding in the interior of a tube mill and will permit the drying and grinding at the respective most favorable conditions.

It is still another object of this invention to provide a method and device as set forth above which will permit .the drying and grinding, especially of very moist, sticky material while making use of low temperature waste gases.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGURES l to 3 diagrammatically illustrate three dif- ,ferent designs of tube mills for carrying `out the method according to the present invention;

FIGURE 4 is a diagrammatic illustration of an entire drying-grinding plant.

FIG. 5 is a modification `over the arrangement of FIG. 4.

FIG. 6 is a transverse section through the drying chamber, said section being taken along the line A-B of FIG. l.

FIG. 7 is a view upon the slot wall of FIG. 1 as seen from the right-hand side of FIG. 1.

The present invention consists primarily in carrying out the two operations, viz. the drying and grinding, independently of each other in -a tube mill in such a way that the waste gases of the drying chamber will not affect the grinding chamber. To -this end, the grinding mill is, along the length thereof, subdivided into a drying chamber and a grinding chamber, While the drying chamber is not filled with grinding bodies but is equipped with lifting elements. Interposed between the said two chambers there is the gas discharge and the material discharge. While, in conformity with the heretofore known practice, the waste gases and the material to be ground are introduced axially in direct current or flow in the same direction, they are no longer passed together through the [grinding chamber. Instead, the gas is already at the end of the drying chamber Withdrawn from the tube mill in radial direction.

For the further processing of the material discharged from the drying chamber and to be ground, there are available two possibilities:

(a) The material pre-dried in the drying chamber will, without bei-ng ground, leave the tube mill and will subsequently be charged into a hammer mill in which the material will be granulated. From the hammer mill the material together with the fine material from the grinding chamber passes to the sifter or directly to the grinding chamber of the tube mill. In the hammer or impact mill the material may, if necessary, be subjected a second time to the drying gases. At the end of the fine grinding chamber, rthe material is again discharged from the tube mill and then passes to a non-heated sifter which separates the finished powder, meal or flour from the grit, which latter is returned to the grinding chamber.

(b) The materia-l is, from the drying chamber passed into the first grinding chamber-granulating chamber-of the tube mill while possibly before, the fine material is separated and together with the material to be ground from the second grinding chamber-fine grinding chamber, is passed to the sifter. This combination makespossible the exploitation of large voluminae of low-temperature waste gases because the drying is possible at three locations, viz. in the drying chamber of the tube mill, of the hammer mill, and in the grinding chamber of the tube mill. The above-mentioned difficulties cannot occur for the following reasons:

(l) The pre-drying of the moist tor possibly sticky material is effected in a uniform flow, which is most favorable for the drying of moist, sticky material. The drying effect is increased by the. strong lifting and dropping movement of the material in view of the high speed of the mill. Thus, no sticking or clogging will occur.

(2) Also in the hammer mill, which subsequently brings about a further drying a-nd the granulation, no sticking or other disorders can occur because the material has, due to being pre-dried, los-t its stickiness.

(3) The sifter -is free from any drying work. It does not have to process too coarse material. In other words, the sifter serves solely its proper purpose, viz. its sifting purpose.

(4) For the drying and grinding chamber there may be selected the respective most favorable speed of the gaseous medium passing through the respective chamber.

From the above, it will be evident that one of the outstanding advantages of the invention consists in that the drying and grinding in the interior of the tube mill will be carried out as economically as possible and under the respective most favorable conditions for the drying and grinding. In addition to saving energy, due to relieving the grinding chamber from too strong a gas iiow, the drying and grinding, especially of very moist, sticky material and the employment 'of low-temperature, moist gases will be possible, so that the invention represents a considerable advance in the art.

Referring now to the drawing in detail, the arrangement shown therein represents a tube mill having a drying chamber 2 into which the moist material to be ground is charged at 1. Rotatable lifting blades 3 on the inside of of the drying chamber 2 bring about a very'intensive engagement of the material in chamber 2 with a drying gas introduced into chamber 2 through an inlet conduit 4. This drying gas is withdrawn from the tube mill through openings 5 at the tube mill portion 6. A portion of the material drops through the openings 5 into a housing 7 and is discharged through the discharge conduit 8. Another portion of the material leaves the fine grinding chamber 9 through the slot wall 10 and combines with the material in the drying chamber 2 -so as, together with the latter, to leave the device through the discharge connection or conduit 8. The total iiow of the material will, with this particular design, 4be passed to a sifter. The coarse particles separated by the sifter are at 11 charged into the fine grinding chamber 9. The fine grinding chamber 9 communicates with a conduit 12 adapted to be charged with fresh air or, if necessary, also with warm gas or warm air.

FIG. 2 shows a modification over the arrangement of FIG. l. According to this modification, the material is charged at 1 into the drying chamber 2 and is discharged through openings 5. The waste gas of the drying chamber 2 is also in this instance withdrawn at the end of said drying chamber without the necessity that it has to pass through the fine grinding chamber 9. The milled material in the fine grinding chamber 9 is, however, not combined with the material from the drying chamber 2, but both fiows of material are held separate and are separately discharged through the two discharge conduits 7' and 7". The material from the fine grinding chamber 9 passes through the slot wall 10 and the openings 5 into a separate discharge housing 7 The method according to the present invention offers the possibility of feeding the material from the drying chamber 2 into a hammer mill or impact mill of any standard type, or the like, if the material is too coarse for grinding in the fine grinding chamber 9. The thus transferred material is then granulated in said hammer or impact mill or, if desired, may be post-dried and then subjected to sifting and post-grinding. The milled material from fine grinding chamber 9 is expediently combined with the material from the hammer mill, is then sifted, and the sifted-out coarse portion is introduced into the fine grinding chamber 9 at 11 and finish-ground.

The method according to the invention may also be employed in connection with a tube mill of the type shown in FIG. 3 in which the material to be ground is adapted to pass to a granulating chamber and subsequently into a second grinding chamber, viz. the fine grinding chamber. The moist material to be ground is charged at 1 into the drying chamber 2. Also in this instance, rotatable lifter blades 3 bring about an intensive engagement of the material with the drying gases which enter at 4 and are discharged or withdrawn through the openings 5 and discharge conduit 6. The material leaving the drying chamber 2 passes through a sifting cylinder 13 and is then conveyed from lifting wall 14 into the rst grinding chamber -granulating chamber 15. The fine material passes through openings 5 into the collecting housing 7. At the end of the-first grinding chamber 15-representing the pre-granulating chamberthe material together with the material from the second grinding chamber 9-fine grinding chamber--is discharged through slot walls 16, 10 and openings 17 into the collecting housing v7. The three flows Iof material and, more specifically, the fine material from the drying chamber 2, the pre-granulated material from the first grinding chamber 15, and the postground material from the fine grinding chamber 9 are withdrawn through conduit 8 and are conveyed to a common sifter (not illustrated). The coarse portion leaving the sifter is introduced into the fine grinding chamber 9 at 11 whereby the circuit of the drying-grinding operation is closed. The charge of the tube mill with drying gas and fresh air is effected in the above-described manner.

However, in this instance, it is to be noted that an additional control member 18 is provided in the discharge connection 6 in order to control the speed of the flowing gaseous media in the various chambers, in conformity with the respective requirements.

An example of a drying-grinding plant for carrying out the method according to the present invention is illustrated in FIG. 4. The moist material to -be ground is charged into a funnel 1 from where it passes onto a conveyor 19 which in its turn feeds the material into the tube mill 20. Arranged within the drying chamber 2 are movable lifter blades 3 which produce a considerable turbulence of the material in the tube mill 20 so as to intimately subject the material to heating gases introduced into the drying chamber 2. The thus pre-dried material is by means of a bucket conveyor 21 conveyed to the heated hammer mill 22. A conveyor worm 23 conveys the finish or nearly finish-dried material to the fine grinding chamber 9 of the tube mill 20. The milled material is received by a bucket conveyor 24 which discharges the milled material into a sirter 25. The grit from the sifter 25 passes together with the material from the hammer mill 22 to the fine grinding chamber 9 of the tube mill 20, whereas the finished material or powder is in a gas ow withdrawn from the sifter 25 and is separated in a cyclon 26, while the remainder is separated in the de-duster 27 and obtained as finished material.

The supply of the milling plant with drying gases is illustrated in the drawing. More specifically, on the lefthand side of FIG. 4 the drying gas, for instance, flue gas of a rotary kiln, is introduced into the milling plant through a conduit 28. The intermediate `branch 4 of conduit 2S passes the drying gas into the drying chamber 2 of the tube mill 20. The upper branch 29 of conduit 28 supplies the hammer mill 22 with drying gas, whereas the lower branch 3d offers the possibility of supplying also the fine grinding chamber 9 additionally with drying heat. The intermediate portion of the tube mill 2t) is surrounded -by a collector housing 7 which on one hand makes possible the discharge of the milled material, and on the other hand permits the withdrawal of the fiue gases. The waste gases from the hammer mill 22 and tube mill 2t) are combined in a sifter 25 and are withdrawn therefrom through cyclon 26 and de-duster 27 and are discharged into the atmosphere. The employment of the waste gases of the milling plant as sifting medium greatly simplifies the method according to the present invention.

In order further to improve the efficiency of the plant, it is also possible to add additional devices. Thus, for instance, below the hammer mill 22 there may be provided shifting means for sifting the broken-up material. The coarser portion of the material may be charged into the fine grinding chamber 9 of the tube mill 20 through the intervention of a worm 23, whereas the finer portion of the material may by means of any standard conveyor be conveyed to the bucket conveyor 24. In this way this finer portion will first pass through sifter 25. Also in this way the already finished flour, meal, or powder is withdrawn from the fine material portion from the hammer mill 22, and only the grit is again conveyed to the fine grinding chamber 9.

Instead of the foreign-vented'sifters ZS-as provided in FIG. 4--it is, of course, also possible to provide a turbo-sitter with a blowing or venting device of its own. In this instance, it is necessary to equip the withdrawal conduit for the waste gases of the mill with a grit separator in order to assure that the line material obtained in the de-duster will not contain particles or grains beyond a certain predetermined size. The grit from the grit separator is, in a manner known per se, again conveyed to the fine grinding chamber 9 of the tube mill 20.

Instead of sifting the product of the hammer mill 22, or additionally to the above-mentioned sifting operation, the material discharged from the drying chamber 2 of the tube mill 20 may be sifted, and the fine material may be conveyed to the sifter 25 leading to the bucket conveyor 24, whereas the coarse portion is conveyed to the bucket conveyor 21 conveying the material to the hammer mill 22.

If it is desired to process a moist material to be ground which has a particular tendency to stick and adhere, a partial flow ofthe material broken up by the hammer mill 22 and dried in the drying chamber 2 may be conveyed to the tube mill 22 together with the sticky, moist material. In this way, the moist material is covered with powder and sticking will more likely be avoided.

It is, of course, to be understood that the present invention is, by no means, limited to the particular methods and arrangements set forth above, but also comprises any modifications within the scope of the appended claims.

What We claim is:

1. A method of grinding moist material in a tube mill having drying chamber means and separate grinding chamber means, which includes the steps of: charging moist material to be ground into said drying chamber means, passing a first flow of gas in the form of a drying gas into and through said drying chamber means while withdrawing the gas having passed through said drying chamber means so as to bypass and grinding chamber means, conveying predried material into said grinding chamber means for grinding therein while independently of said first flow of gas passing a second flow of gas through said grinding chamber means.

2. A method according to claim 1, which includes the steps of: sifting the material dried in said drying chamber means for separating the ne material from the coarse material, and conveying the coarse material to said grinding chamber means.

3. A method -according to claim 1, which includes the steps of: in addition to charging moist material to be ground into said drying chamber means also charging pre-dried material of the type of said material to be ground into said drying chamber means.

4. A method according to claim 1, which includes the steps of: rough grinding the material dried in said drying chamber means outside said drying chamber means, separating from the thus rough ground material those particles which exceed a desired maximum grain size, and subsequently fine grinding the said separated particles.

5. A method according to claim 4, which includes the steps of conveying a portion of the fine-ground material to the drying chamber.

6. A method according to claim 4, which includes the step of: employing the drying gas withdrawn from the drying chamber means for aiding in the separation from the rough-ground material of those particles which exceed said desired maximum particle size.

7. A mill for separately drying and grinding material, which includes: a tubular housing having a first section adapted to be connected to a source of drying gas and forming a drying chamber only, said tubular housing also having a second section separated from said drying chamber and forming a grinding chamber for grinding material received by and dried in said drying chamber, said tubular housing furthermore having a third section located between said first and said second section and comprising apertures for communication with said drying chamber and said grinding chamber, first conduit means in flow communication with said third section and bypassing said second section for withdrawing gas passed through said first section and causing said drying gas to bypass said second section, and second conduit means independent of said first conduit means and in fiow communication with said second section for conveying a iiow of gas thereinto.

8. A mill according to claim 7, in which said third section is surrounded by an annular housing having said first conduit means connected thereto.

9. A mill according to claim 7, in which said third section is provided with first apertures communicating with both the interior of said drying chamber means and the interior of said grinding chamber means for discharging material treated in said rst and second sections, said third section also being provided with second apertures communicating with both the interior of said first and second sections for discharging drying gas from said drying chamber means and gaseous substance from said grinding chamber means, first discharge means communicating with and common to said first apertures, and second discharge means communicating with and common to said second apertures.

10. A mill according to claim 7, in which said third section is provided with a first and second group of apertures respectively communicating with the interior of said first and second sections, and in which said first conduit means communicates through apertures of said first group with the interior of said first section for discharging dried material therefrom, and additional conduit means communicating through apertures of said second group with the interior of said second section for discharging ground material therefrom, and further conduit means communicating through apertures of said firstand second group with the interior of said first and second sections for discharging drying gas from said first section and gaseous substance from said second section.

11. A mill for separately drying and grinding material, which includes: a tubular housing having a first section forming a drying chamber only for exclusively drying a moist charge received therein, said first section being provided with first inlet means for feeding thereinto a moist charge to be dried and drying gas for drying said moist charge, said tubular housing also having a second section separated from said drying chamber and representing a fine grinding chamber for ne'grinding material dried in said drying chamber, said fine grinding chamber having second inlet means for admitting thereinto a dried charge to be ground and a gaseous substance, said tubular housing having an additional section interposed between said drying chamber and said fine grinding chamber and forming a coarse grinding chamber for coarse-grinding material from said drying chamber, screen means interposed between said drying'chamber and said coarse grinding chamber and for conveying dried material from said drying chamber to said coarse grinding chamber, first discharge means communicating with said screen means for discharging fine material passed through said screen means toward the outside thereof, second discharge means communicating With said coarse grinding chamber for discharging coarse-ground material therefrom and also for discharging finely ground material from said fine grinding chamber, first means common to said first and second discharge means for connection with a sifter, and second means communicating with the interior of said drying chamber and said fine grinding chamber for respectively discharging therefrom drying gas and gaseous material.

12. An arrangement according to claim 11, which includes control means arranged in said second means for controlling the flow of gaseous substance from said fine grinding chamber therethrough.

References Cited by the Examiner UNITED STATES PATENTS 2,347,215 4/ 1944 Pattee 241-8 2,350,162 5/1944 Gordon 34-10 2,351,870 6/1944 Newhouse 241-54 2,609,299 9/1952 Singer 241-11 X 3,117,868 1/1964 Madrazo 241--8 X FOREIGN PATENTS 369,330 .3/1932 Great Britain.

WILLIAM W. DYER, JR., Primary Examiner.

H. F. PEPPER, Assistant Examiner. 

1. A METHOD OF GRINDING MOIST MATERIAL IN A TUBE MILL HAVING DRYING CHAMBER MEANS AND SEPARATE GRINDING CHAMBER MEANS, WHICH INCLUDES THE STEPS OF: CHARGING MOIST MATERIAL TO BE GROUND INTO SAID DRYING CHAMBER MEANS, PASSING A FIRST FLOW OF GAS IN THE FORM OF A DRYING GAS INTO AND THROUGH SAID DRYING CHAMBER MEANS WHILE WITHDRAWING THE GAS HAVING PASSED THROUGH SAID DRYING CHAMBER MEANS SO AS TO BYPASS AND GRINDING CHAMBER MEANS, CONVEYING PREDRIED MATERIAL INTO SAID GRINDING CHAMBER MEANS FOR GRINDNG THEREIN WHILE INDEPENDENTLY OF SAID FIRST FLOW OF GAS PASSING A SECOND FLOW OF GAS THROUGH SAID GRINDING CHAMBER MEANS.
 7. A MILL FOR SEPARATELY DRYING AND GRINDING MATERIAL, WHICH INCLUDES: A TUBULAR HOUSING HAVING A FIRST SECTION ADAPTED TO BE CONNECTED TO A SOURCE OF DRYING GAS AND FORMING A DRYING CHAMBER ONLY, SAID TUBULAR HOUSING ALSO HAVING A SECOND SECTION SEPARATED FROM SAID DRYING CHAMBER AND FORMING A GRINDING CHAMBER FOR GRINDING MATERIAL RECEIVED BY AND DRIED IN SAID DRYING CHAMBER, SAID TUBULAR HOUSING FURTHERMORE HAVING A THIRD SECTION LOCATION BETWEEN SAID FIRST AND SAID SECOND SECTION AND COMPRISING APERTURES FOR COMMUNICATION WITH SAID DRYING CHAMBER AND SAID GRINDING CHAMBER, FIRST CONDUIT MEANS IN FLOW COMMUNICATION WITH SAID THIRD SECTION AND BYPASSING SAID SECOND SECTION FOR WITHDRAWING GAS PASSED THROUGH SAID FIRST SECTION AND CAUSING AND DRYING GAS TO BYPASS SAID SECOND SECTION, SAID SECOND CONDUIT MEANS INDEPENDENT OF SAID FIRST CONDUIT MEANS AND IN FLOW COMMUNICATION WITH SAID SECOND SECTION FOR CONVEYING A FLOW OF GAS THEREINTO. 